The expression of polypeptides fused to the surface of filamentous bacteriophage provides a powerful method for recovering a particular sequence from a large ensemble of clones (Smith et al., Science, 228:1315-1517, 1985). Peptides binding to avidin or antibodies have been selected from large libraries by the relatively simple method of panning (Scott et al., Science, 249:386-290, 1990; Devlin et al., Science, 249:404-406, 1990; and Cwirla et al., Proc. Natl. Acad. Sci. U.S.A., 87:6378-6382, 1990). Larger proteins, such as antibodies (McCafferty et al., Nature, 348:552-554, 1990; Lowman et al., Biochemistry, 30:10832-10838, 1992; and Kang et al., Proc. Natl. Acad. Sci. U.S.A., 88:4363-4366, 1991) and human growth hormone (Bass et al., Proteins, 8:309-314, 1990), have also been fused to surface proteins of filamentous phage which can then be used for the selection of particular sequences from a large number of variants.
In these filamentous phage systems, the foreign protein or polypeptide is fused to the amino-terminus of either coat protein III or coat protein VIII of the filamentous phage M13 and the fused protein is secreted through the Escherichia coli cytoplasmic membrane into the periplasmic space. Most of the proteins successfully fused with filamentous phage surface proteins have been secreted proteins and, although Rebar and Pabo (Science, 263:671-673, 1994) have recently used pIII to display three zinc fingers of Zif268 (a DNA-binding protein), many cytoplasmic proteins will interfere with the passage of the fusion product from the cytoplasm to the periplasm.
Furthermore, cDNA gene products cannot be directly expressed as fusion proteins to the amino-terminus of the viral coat proteins due to transcriptional stop sites present at the 3′ end of non-translated regions in eukaryotic cDNA obtained by poly(A+) selection of mRNA followed by poly(A) priming (Molecular Cloning: A Laboratory Manual, Second Edition, Maniatis et al., eds., Cold Spring Harbor, N.Y., 1989). These facts prevent the use of filamentous phage systems developed thus far for cDNA library screening.
Herein described is a lambda vector system useful for the expression of a foreign protein on its surface which should be more appropriate for proteins that fold in the cytoplasm. The lambda vector of this invention could therefore complement the filamentous phage system in the identification of novel polypeptides with a biological activity.